Magnetic Sensitivity Class Description Report Raw Data Magnetic Sensitivity Summary [Updated 7/31/07] The Urantia Book asserts that all animals have at least a limited sense of direction due to magnetic forces on the planet that "activate the hosts of microscopic bodies" "which are sensitive and responsive to these directional currents. . . This sense is not wholly wanting as a conscious possession by mankind. These bodies were first observed on Urantia about the time of this narration." The observation of a mechanism in sharks that is sufficiently sensitive to detect the earth's magnetic field was made at "about the time of this narration," the mid 1930's. After The Urantia Book was published in 1955, scientists discovered the presence of biologically produced magnetite in a variety of animals, including humans. Magnetite is the most magnetically sensitive material on earth. Sensitivity to the earth's magnetic field in a variety of migratory animals is now a well established fact of science. Though human sensitivity to the earth's magnetic field is still debated within the scholarly community, some researchers are confident that sufficient evidence already exists to make this claim.

Magnetic Sensitivity: Class A Topic
[Updated 10/11/07]

The Urantia Book states that all organisms have a biologic sensitivity to the earth's magnetic field and that this sensitivity is right on the edge of human consciousness. At the time of its publication, scientists did not generally believe that biologic organisms could have a mechanism that is sensitive to such a subtle electromagnetic field. Now many migrating animals have been found to possess such sensitivity and some researchers assert that human beings also can sense the earth's magnetic field.

The Urantia Book asserts that the “bodies” responsible for this sensitivity were being discovered right around the time of The Urantia Book's narration, which it asserts was in the mid 1930's. In the mid 1930's scientists did discover that ampullae in a sharks snout had tiny inner ear type hairs and that there were nerves running from these ampullae to the brain. They could also tell that sharks were sensitive to electric fields. But it took until the 1960's, over five years after The Urantia Book's publication, to discover that the mechanism in these ampullae were extremely sensitive to electromagnetic fields.

Additionally, in the 1960's it was discovered that many animals, including humans, produce a substance called “magnetite,” which is the most magnetically sensitive substance on earth. Magnetite produced in biologic organisms is shaped more cubically than octagonally (the way it otherwise occurs in the mineral world), which allows these tiny particles to line up like bar magnets within cells. It was previously believed that biologic organisms could not produce this substance.

This report just barely makes it into the Class A category. However, advancements in this field are clearly headed in the direction of lending additional support to this report.

Magnetic Sensitivity Report
[Updated 7/31/07]
Prepared by Halbert Katzen, JD with special thanks to Phil Calabrese, PhD and Fred Harris

Before addressing the particular scientific advances that having been catching up to The Urantia Book's statements about the sensitivity of humans and other organisms to the earth's magnetic field, some context needs to be provided regarding the assertions made by the authors of The Urantia Book about the limitations and permissions that were placed upon them in preparing scientific material for the book. On the one hand The Urantia Book says,

"The laws of revelation hamper us greatly by their proscription of the impartation of unearned or premature knowledge. . .Mankind should understand that we who participate in the revelation of truth are very rigorously limited by the instructions of our superiors. We are not at liberty to anticipate the scientific discoveries of a thousand years." (Urantia Book 101:4.1,2)

On the other hand, The Urantia Book says,

"Let it be made clear that revelations are not necessarily inspired. The cosmology of these revelations is not inspired. It is limited by our permission for the co-ordination and sorting of present-day knowledge. . .

"While statements with reference to cosmology are never inspired, such revelations are of immense value in that they at least transiently clarify knowledge by:

1. The reduction of confusion by the authoritative elimination of error.
2. The co-ordination of known or about-to-be-known facts and observations."

Striking a balance between not "anticipating the discoveries of a thousand years" and "the co-ordination of known or about-to-be-known facts and observations" is something that would have had to have been done regarding the issue of biological sensitivity to the earth's magnetic field. The initial phases of scientific study on this issue certainly began before The Urantia Book was published, and today scientific opinion on the subject still lacks a broad consensus. Nonetheless, the pattern of emerging science is well aligned with The Urantia Book's assertions on this topic. The early research that was done prior to The Urantia Book's publication has advanced significantly in the last several decades.

Whether human beings can be consciously sensitive to the earth's magnetic field is not a settled question in science. However, the ongoing research in this area is pointing in that direction the way a compass needle points north. Some researchers already conclude that sufficient evidence exists for the assertion that human beings have this capability to some degree.

Wikipedia's provides a brief encapsulation of the subject and a quick appreciation for the basic issues related to this report.

"Magnetoception (or "magnetoreception") is the ability to detect changes in a magnetic field to perceive direction or altitude and has even been postulated as a method for animals to develop regional maps. It is most commonly observed in birds, though it has also been observed in many other animals including honeybees and turtles. Researchers have identified a probable sensor in pigeons: a small (dwarf), heavily innervated region of the skull, which contains biological magnetite. Humans have a similar magnetite deposit in the ethmoid bone of the nose. Although there is no dispute that a magnetic sense exists in many avians (it is essential to the navigational abilities of migratory birds), it is a controversial and not well-understood phenomenon. . . In bees, it has been observed that magnetite is embedded across the cellular membrane of a small group of neurons; the theory is that when the magnetite aligns with the Earth's magnetic field, induction causes a current to cross the membrane which depolarizes the cell."¹

Could it be that all we have to do to find magnetic north is follow our nose? The Urantia Book makes the following statements regarding a sense of direction and orientation:

"The four points of the compass are universal and inherent in the life of Nebadon [the section of the cosmos where Earth exists]. All living creatures possess bodily units which are sensitive and responsive to these directional currents. These creature creations are duplicated on down through the universe to the individual planets and, in conjunction with the magnetic forces of the worlds, so activate the hosts of microscopic bodies in the animal organism that these direction cells ever point north and south. Thus is the sense of orientation forever fixed in the living beings of the universe. This sense is not wholly wanting as a conscious possession by mankind. These bodies were first observed on Urantia [Earth] about the time of this narration." (Urantia Book 34:4.10)

The Urantia Book claims that its content was provided in the mid 1930's; however, it was not published until 1955. Though the publication date is a universally uncontenscious issue, it's claim that the content of The Urantia Book was provided in the mid 1930's is an issue that attracts a broader range of opinion and is not so easily verified as the book's publication date. Notwithstanding that various forms of evidence exist to support the mid 1930's date, the accuracy of this date is not what is at issue here. The date is relevant because it provides a way to investigate the internal consistency of The Urantia Book. Because the text refers to the "time of this narration," presumably the mid 1930's date, and not the publication date, reflects the intended meaning.

If there were no evidence of the discovery in the mid 1930's of "bodies" that are sensitive to the earth's magnetic field, this lack of evidence would have to weigh against the credibility of The Urantia Book. But such is not the case. However, to The Urantia Book's credit, the observations of the mid 1930's, as will be shown, were not at all conclusive about sensitivity to the earth's magnetic field. They simply found a mechanism in sharks that was highly sensitive to electromagnetic fields. Therefore, The Urantia Book authors did risk loosing credibility if the observations in the mid 1930's were not later tied to issues regarding sensitivity to the earth's magnetic field.

However, before reviewing scientific discoveries on this subject, it is important to first provide some general information on the relationship between electricity and magnetism. This is necessary in order to appreciate why the jargon in this topic switches from "electroreceptors" to "magnetoreceptors."

"Electromagnetism is the physics of the electromagnetic field: a field which exerts a force on particles that possess the property of electric charge, and is in turn affected by the presence and motion of those particles.

"The magnetic field is produced by the motion of electric charges, i.e. electric current. The magnetic field causes the magnetic force associated with magnets.

"A changing magnetic field produces an electric field (this is the phenomenon of electromagnetic induction, the basis of operation for electrical generators, induction motors, and transformers). Similarly, a changing electric field generates a magnetic field. Because of this interdependence of the electric and magnetic fields, it makes sense to consider them as a single coherent entity—the electromagnetic field."²

With that understanding we can now proceed with appreciating scientific developments that are harmonious with The Urantia Book's assertion that observations were made in the mid 1930's related to biological mechanisms that would later be discovered to be sensitive to the earth's magnetic field.

In the History of Electroreceptors section of Faramarz Samie's paper titled Electroreception in Elasmobranchs he states:

"The first evidence of electrosensitivity in elasmobranchs dates back to 1935 when Dijkgraaf, working on Scyliorhinus canicula, noticed the animal's sensitivity to a rusty steel wire (Dijkgraaf & Kalmijn, 1962). The experimenters approached the head of a blindfolded shark with such a wire. They observed that the animal escaped when the wire was closer than several centimeters from its head. They repeated the experiment with a glass rod, but the animal did not react to it. Dijkgraaf assumed that the shark was stimulated by the galvanic currents produced at the surface of the metal wire, but had no way of proving his assumption.

"Dijkgraaf's hypothesis largely remained a speculation until Lissmann in 1958 formally suggested, based on behavioral evidence, that a group of receptors and central processes, called the ampullae of Lorenzini, aid in the detection and analysis of electric fields in the marine environment of fish. Later, experimenters verified the existence of the new class of specialized receptors through physiological experiments. They named them "electroreceptors" because their adequate stimuli were electric fields (Bullock et al. 1961, Kalmijn, 1966, 1971)."³

The Shark's Electric Sense article in the August 2007 edition of Scientific American provides additional information on the history of the discovery of electromagnetic sensitivity in animals.

"The story begins in 1678, when Italian anatomist Stefano Lorenzini described pores that speckled the forward part of the head of sharks and rays, endowing them with something resembling a bad five-o'clock shadow. He noted that. . .each opening led to a long transparent tube that was filled with a crystalline gel. Some of the tubes were small and delicate, but others were nearly the diameter of a strand of spaghetti and several inches in length. . .

"By the late 19^th century the newly improved microscope revealed that the pores on a shark's snout and the unusual structures underneath them, today called ampullae of Lorenzini, must be sensory organs of some kind. . .

"A thin nerve emerged from the ampulla and joined branches of the anterior lateral line nerve. Scientists traced these nerve fibers to the base of the skull, where they enter the brain through the dorsal surface of the medulla, a destination characteristic of nerves that carry sensory information into the brain. Observers discerned a single tiny hair cell, similar to those of the human inner ear and of a fish's lateral line system, inside each ampulla. The type of stimulus they might detect remained unknown, however. . .

"In 1938 Alexander Sand of the Marine Biological Association of Plymouth, England, succeeded in amplifying and recording nerve pulses running from ampullae of Lorenzini to the brain. . . In the early 1960s biologist R. W. Murray of the University of Birmingham in England repeated Sand's experiments with modern electrophysiological instruments and confirmed the responses to temperature changes, pressure differences and touch, but he also observed that the organs were sensitive to slight variations in salinity. Moreover, when he happened to switch on an electric field near the opening of a tube connected to an ampulla, the firing pattern changed. Further, the pattern altered according to the intensity and polarity of the field. When the field's positive pole neared the opening of an ampulla, the firing rate declined; when the negative pole came near, firing increased.

"Astonishingly, Murray determined that the organs could respond to fields as weak as one millionth of a volt applied across a centimeter of seawater. This effect is equivalent to the intensity of the voltage gradient that would be produced in the sea by connecting up a 1.5 volt AA battery with one pole dipped in the Long Island Sound and the other pole in the waters off Jacksonville, Florida. Theoretically, a shark swimming between these points could tell when the battery was switched on or off."

This discovery in the mid 1930's of some of the functional characteristics of the ampullae of Lorenzini is in harmony with The Urantia Book's statement that the "bodies were first observed on Urantia about the time of this narration." Also consistent with The Urantia Book's assertion that its authors "are not at liberty to anticipate . . . scientific discoveries," is that there is no mention of magnetite being present in biologic organism, as this was not discovered until after The Urantia Book's publication in 1955.⁴ Additional discoveries were made within the ten years following publication of The Urantia Book that took this type of research to the next level. The conclusion regarding magnetic sensitivity is given by The Urantia Book, but the details are withheld. This could be the type of about-to-be-discovered knowledge that the authors indicate is within the permissible range of providing revelatory information.

"In the 1960s, Caltech paleoecologist Heinz Lowenstam startled biologists and geologists alike with the discovery that many animals do what conventional science had considered impossible: they manufacture substances such as the iron-containing mineral magnetite within their bodies. Out of Lowenstam's work came the more recent finding that many migratory animals, including birds, bees, and whales, generate magnetite within their bodies and may owe their uncanny homing instincts to the presence of this "internal compass" that allows them to navigate by means of Earth's magnetic field."⁵

The discovery of magnetite in numerous migrating species supports The Urantia Book's assertion that a general ability to detect direction exists throughout the spectrum of biological organism.

Magnetite is the world's most magnetic substance. In the article Biomagnetism and Bio-Electromagnetism: The Foundation of Life H. Coetzee, Ph.D. further explains the importance of this discovery.

"The discovery of a biogenic material (that is, one formed by a biological  organism) with ferromagnetic properties [the ability to maintain magnetic properties without an outside electric current being applied] and found to be magnetite was the first breakthrough toward an understanding as to why some animals have the ability to detect the earth's magnetic field. Searches for biogenic magnetite in human tissues had not been conclusive until the beginning of the 1990's when work with high-resolution transmission electron microscopy and electron diffraction on human brain tissue extracts of the cerebral cortex, cerebellum, and meninges (membranes surrounding the brain and spinal cord) identified magnetite-maghemite crystals.

Magnetite Crystals under Low Magnification

"These magnetite crystals were found to be organized into linear, membrane-bound chains a few micrometers in length, with up to 80 crystals per chain. Furthermore individual crystals have their magnetite-maghemite aligned along the length of the chain axes (the "easy" direction of magnetization). The magnetite-maghemite crystal alignment has been interpreted as a biological mechanism for maximizing the magnetic moment per particle, as the magnetite-maghemite direction yields approximately 3% higher saturation magnetization than do other directions. This prismatic particle shape is also uncommon in geological magnetite crystals of this size, which are usually octahedra. The crystal morphology was found to be cubo-octahedral with the magnetite-maghemite faces of adjacent crystals lying perpendicular to the chain axis.

"All the magnetite crystals that have been examined to date are single magnetic domains, which means that they are uniformly and stably magnetized and have the maximum magnetic moment per unit volume possible for magnetite. Elemental analysis, by energy-dispersive X-ray analysis, electron diffraction patterns, and high resolution transmission electron microscopy lattice images, showed that many of the particles were structurally well-ordered and crystallographically single-domain magnetite. This means that the production of this biomineral must be under precise biological control.

"Ferromagnetic crystals interact more than a million times more strongly with external magnetic fields than do diamagnetic or paramagnetic materials (deoxyhemoglobin, ferritin, and hemosiderin). With this finding researchers were posed with a fundamental question for biology, namely: What is the mechanism through which the weak geomagnetic fields are perceived by organisms that are able to precipitate crystals of a ferromagnetic mineral such as magnetite (Fe3O4)? Could these crystals use their motion in a variety of ways to transduce the geomagnetic field into signals that can be processed by the nervous system?

"The presence of membrane-bound biomineral magnetite, which has been shown to have a biological origin, and the implication that some kind of mechanical coupling must take place between each compass magnetite particle and a mechanoreceptor, or at least a functionally equivalent mechanism allowing the position of the particle to be monitored by a sensory organelle in the body, is unique. Research has also found that the magnetite is produced by the cells of the organism when needed. Forms of advanced physical intelligence can directly tap into this information if they have a crystalline network within their brain cavity.

"Scientists are now asking the fundamental question: What is magnetite doing in the human brain? In magnetite-containing bacteria, the answer is simple: Magnetite crystals turn the bacteria into swimming needles that orient with respect to the earth's magnetic fields. Magnetite has also been found in animals that navigate by compass direction, such as bees, birds, and fish, but scientists do not know why the magnetite is present in humans, only that it is there."⁶

Above: A linear chain of biogenic magnetite crystals, extracted from tissues in the frontal region of the sockeye salmon, Oncorhynchus nerka, a close relative of the rainbow trout, Oncorhynchus mykiss. These are also single magnetic domains, with crystal alignments similar to those in magnetotactic bacteria. (Photo credit: S. Mann)

Even though scientists have discovered biogenic magnetite in animals, there still remains the question of whether and how such bodies could actually stimulate the brain in order to provide directional information. In the late 1990's results began to be published out of the University of Auckland of experiments that showed nerves connecting regions in both the skull and the nose of rainbow trout where magnetite is produced.⁷

"Since magnetite had been previously found in trout's skulls, the investigators decided to record neural activity from nerves that innervate the relevant region of the skull. They discovered a population of nerve fibers that respond to changes in the ambient magnetic field in one specific nerve, called the ros V ("ros five" nerve). This is a branch of the trigeminal nerve, which supplies an innervation to the face and skull of all vertebrates, including humans. Dye was used to trace this nerve to the nose of the trout."⁸

"Although this may seem like more than a smoking gun, Dr. Diebel is still cautious. Although she believes these are the long sort-after magneto-receptors, she says they are yet to prove the receptors are actually connected to the nerves. That involves future more complex experiments."⁹

Indeed, some caution in jumping to conclusions may be good advice. On May 14, 2004 Science Daily published an article that brings into to question whether nerves to the brain from locations where magnetite is present are responsible for magnetoreception. An article entitled Following Earth's Magnetic Field: Chemical Reaction In Birds Provides Sense Of Direction During Migratory Flights indicates that magnetite is not necessary. The article, however, seems to jump to conclusions by arguing that magnetite is not involved because it is possible that animals have redundant systems so that they can continue to navigate when one of their systems may not be able to function effectively.

"Migrating birds stay on track because of chemical reactions in their bodies that are influenced by the Earth's magnetic field, a UC Irvine-led team of researchers has found.

"The birds are sensitive even to rapidly fluctuating artificial magnetic fields. These fields had no effect on magnetic materials such as magnetite, indicating that the birds do not rely on simple chunks of magnetic material in their beaks or brains to determine direction, as experts had previously suggested.

"The results are reported in the May 13 issue of Nature. The study is the first to reveal the mechanism underlying magnetoreception the ability to detect fluctuations in magnetic fields in migratory birds.

"In the study, Thorsten Ritz, assistant professor of physics and astronomy, and colleagues exposed 12 European robins to artificial, oscillating magnetic fields and monitored the orientation chosen by these birds. The stimuli were specially designed to allow for responses that could differ depending on whether birds used small magnetic particles on their bodies or a magnetically sensitive photochemical reaction to detect the magnetic field.

"We found that the birds faced in the usual direction for their migration when the artificial field was parallel to the Earth's natural magnetic field, but were confused when the artificial field was applied in a different direction," said Ritz, the lead author of the paper. "Since the artificial field's oscillations were too rapid to influence magnetic materials like magnetite, it suggests that the most likely mechanism for magnetic orientation in these birds involves tiny changes to magnetically sensitive chemical reactions, possibly occurring in the eyes of the birds we are not sure.

"In the experiments, the robins could walk and flutter in their cages but could not fly. The birds oriented well in the Earth's magnetic field alone, but were disoriented in the presence of a broad-band (0.1-10 megahertz) and 7 megahertz oscillating field, aligned at a 24 or 48 degree angle to the Earth's magnetic field. When the same 7 megahertz oscillating field was aligned parallel to the Earth's magnetic field, the robins showed normal migratory orientation again.

"Unlike our senses involving vision, hearing, smell and touch, we do not know what receptors underlie magnetoreception," Ritz said. "Migratory birds have long been known to possess a magnetic compass that helps them find the correct direction during their migratory flights. It has remained unknown, however, how birds can detect the direction of the Earth's magnetic field.

"Now, our study points to what we need to look for a molecular substrate for certain chemical reactions. That is, we can rule out magnetic materials in birds' beaks and elsewhere as being possible candidates. Magnetite in the beaks, however, may play a role in detecting the strength but not the direction of the Earth's magnetic field."

Though the final word is obviously not in on the subject of megnetoreception, some things have been well established. One is that many animals are sensitive to the earth's magnetic field and are able to use this sensitivity for navigation. These findings are increasingly supportive of The Urantia Book's assertion that all organisms have this ability to some degree. Additionally, even though human sensitivity to the earth's magnetic field still remains an open question, there is uncontroversial evidence of the presence in the human body of magnetite and other mechanisms that seem to parallel those found in animals that do exhibit sensitivity to the earth's magnetic field. As well, the way the research has been unfolding is consistent with The Urantia Book's assertion that the specific information it provides must be limited with respect to what has already been discovered, even though the authors are given leeway to provide for the "co-ordination of known or about-to-be-known facts and observations."¹⁰

1 http://en.wikipedia.org/wiki/Magnetoception

2 http://en.wikipedia.org/wiki/Electromagnetism

3 http://wrt-intertext.syr.edu/II2/samie.html

4 Urantia Book 101: 4.2

5 http://www.admissions.caltech.edu/about/milestones

6 http://www.affs.org/html/biomagnetism.html

7 http://www.abc.net.au/science/news/stories/s154625.htm

8 Howard C. Hughes: Sensory Exotica: a world beyond human experience; 1999, Ch. 10

9 http://www.abc.net.au/science/news/stories/s154625.htm

10 Urantia Book 101:4.5

Magnetic Sensitivity Raw Data

Urantia Book 34:4.10

First evidence 1935 http://wrt-intertext.syr.edu/II2/samie.html

Caltech study on human sensitivity http://www.gps.caltech.edu/~jkirschvink/pdfs/KirschvinkBEMS92.pdf

http://jeb.biologists.org/cgi/reprint/70/1/105.pdf

http://en.wikipedia.org/wiki/Magnetoception

http://www.abc.net.au/science/k2/moments/s148725.htm

http://www.affs.org/html/biomagnetism.html

magnetite in brain abstract http://www.biophysics.uwa.edu.au/magnetite.html

magnetite in brain report http://www.pnas.org/cgi/reprint/89/16/7683.pdf

http://www.pubmedcentral.nih.gov/picrender.fcgi?artid=49775&blobtype=pdf

magnetite in humans 1980 http://jeb.biologists.org/cgi/reprint/92/1/333.pdf

1957 animal sensitivity http://www.pbs.org/wgbh/nova/magnetic/animals.html

NOT magnetite http://www.sciencedaily.com/releases/2004/05/040514030725.htm

1947 ApplPhys Yeagley http://scitation.aip.org/getpdf/servlet/GetPDFServlet?filetype=
pdf&id=JAPIAU000018000012001035000001&idtype=cvips&prog=normal

bacteria http://en.wikipedia.org/wiki/Magnetotactic_bacteria

http://www.angel.ekol.lu.se/~rachel/publications/Introductory%20Paper%20def.pdf

images of bacteria w/ magnetite http://aem.asm.org/cgi/content/full/71/8/4902

Biomagnetism and Bio-Electromagnetism: The Foundation of Life http://www.affs.org/html/biomagnetism.html

Nerves in trout connecting nose and brain where magnetite is present http://www.abc.net.au/science/news/stories/s154625.htm

http://wrt-intertext.syr.edu/II2/samie.html

A 1992 Caltech study titled Magnetite in Human Tissues: A Mechanism for the Biological Effects of Weak ELF Magnetic Fields provides additional evidence of this capability that goes beyond the "microscopic bodies" that were discovered in other animals prior to The Urantia Book's publication. The summary of this study concludes that "These structures are "biological bar magnets," with interaction energies with the geomagnetic field exceeding thermal noise (kT). Biogenic magnetite provides easy and well-understood mechanisms for the geomagnetic field to influence processes at the cellular level, and it may also be involved with other cellular functions, such as iron transport or storage." The study also indicates that biogenic magnetite is produced by human beings.

http://en.wikipedia.org/wiki/Magnetoception

Howard C. Hughes: Sensory Exotica: a world beyond human experience; 1999

Discovery of magnetoreception:

First suggested in 1859 by Middendorf

"[F]riedrich Merkel and his students at the University of Frankfurt. . . amassed an impressive body of evidence suggesting that migratory birds do indeed sense some aspect of the Earth's magnetic field, and use this ability to navigate accurately over long distances." Ch. 9, p. 137

"The initial evidence for magnetically based orientation in migratory birds came from a classic experinment by Merkel and Fromme in 1958." p.138

reference to Baker, 1985 "Baker reports that people score above chance at orienting themselves according to compass directions." p. 150

polyester clothing can interfer with magnetic sensitivity, cotton is better p. 150

"But the scientific study of animal navigation is usually said to have begun in the years between 1958 and 1965, when a group of zoologists led by Friedrich Merkel, a professor at the Univeristy of Frankfurt in Germany, made a startling and initially quite controversial discovery." Noticed that birds in enclosed rooms without visual cues aligned toward migration "premigratory restlessness" p.129

Ch. 10 Michael M. Walker and associates at the University of Auckland published results in 1997 of experiments that showed nerves related to magnetite in the nose of trout. "Since magnetite had been previously found in trout's skulls, the investigators decided to record neural activity from nerves that innervate the relevant region of the skull. They discovered a population of nerve fibers that respond to changes in the ambient magnetic field in one specific nerve, called the ros V ("ros five" nerve). This is a branch of the trigeminal nerve, which supplies an innervation to the face and skull of all vertebrates, including humans." Dye was used to trace this nerve to the nose of the trout.

Ch 12 p.204 "And in 1917, two American zoologists, George Parker an dAnne van Heusen, noted that blindfolded catfish resonded quite vigorously to metal rods placed in the water, but did not respond in a similar fashion to glass rods. Parker an dvan Heusen recognized that this effect was probably due to the electrical fields generated by cahimcal reactions between the metal rods and the water; they knew that glass rods could not produce these fields."

Major Huber, Animal Homing and Migration QL 782.5 .H82 1993

Scientific American August 2007: The Shark's Electric Sense

"The story begins in 1678, when Italian anatomist Stefano Lorenzini described pores that specled the forward part of the head of sharks and rays, endowing them with something resembling a bad five-o'clock shadow. He noted that. . .each opening led to a long transparent tube that was filled with a crystalline gel. Some fo the tubes were small an ddelicate, but others were nearly the diameter of a strand of spaghetti and several inches in length. . .By the late 19^th century the newly improved microscope revealed that the pores on a shark's snout and the unusual structures underneath them, today called ampullae of Lorenzini, must be sensory organs of some kind. . .A thin nerve emerged from the ampulla and joined branches of the anterior lateral line nerve. Scientists traced these nerve fibers to the base of the skull, where they enter the brain through the dorsal surface of the medulla, a destination characteristic of nerves that carry sensory information into the brain. Observers discerned a single tiny hair cell, similar to those of the human inner ear and of a fish's lateral line system, iniside each ampulla. The type of stimulus they might detect remained unknown, however. . . In 1938 Alexander Sand of the Marine Biological Association of Plymouth, England, succeeded in amplifying and recording nerve pulses running from ampullae of Lorenzinin to the brain. . . In the early 1960s biologist R. W. Murray of the University of Birmingham in England repeated Sand's experiments with modern electrophysiological instruments and confirmed the responses to temperature changes, pressure differences and touch, but he also observed that the organs were sensitive to slight varioations in salinity. Moreover, when he happened to switch on an electric field near the opening of a tube connected to an ampulla, the firing pattern changed. Further, the pattern altered according to the intensity and polarity of the field. When the field's positive pole neared the opening of an ampulla, the firing rate declined; when the negative pole came near, firing increased. Astonishingly, Murray determined that the organs could respond to fields as weak as one millionth of a volt applied across a centimeter of seawater. This effect is equivalent to the intensity of the voltage gradient that would be produced in the sea by connecting up a 1.5 volt AA battery with one pole dipped in the Long Island Sound and the other pole in the waters off Jacksonville, Florida. Theoretically, a shark swimming between these points could tell when the battery was switched on or off."

http://wrt-intertext.syr.edu/II2/samie.html

Electroreception in Elasmobranchs

Faramarz Samie

• As a bioengineer I learn to apply mathematical, chemical, and physical concepts to the analysis of biological systems. In the Writing 405 course that I took with Roberta Kirby-Werner, I was given an opportunity to address research issues in my discipline in a formal project. I chose to analyze electroreception, a sensory modality that enables sharks and other animals to perceive electric fields, and wrote a professional-technical paper in which I reported my findings. I studied electroreception because of the insight it gives into the life of animals that perceive the world in a way that we cannot. It also teaches us about identifying and classifying receptors. My objective for this particular paper was to make some of the technical concepts in my discipline accessible to a more general audience which possesses an interest in science.

Sharks, rays, and skates make up a scientific grouping of fish called elasmobranchs. Unlike vertebrates, these animals have a cartilaginous skeletal system. The earliest record of this group dates back over 450 million years. In fact, their fossil records date back more than twice that of the dinosaurs. Without question, they are among the most feared animals on earth. Few acts of brutality committed by humans can top the terror that a Great White shark strikes into the hearts of men and women. In keeping with the Hollywood image of sharks (License to Kill, Jaws, Jaws II, and Jaws III), many people see sharks as mindless eating machines that create havoc upon sensing the smallest drop of blood. This image is incorrect. Elasmobranchs are feared because they are misunderstood.

Elasmobranchs, through the processes of natural selection, have adapted to live and survive in the earth's oceans and seas. They are one of the most dominant predators in their domain although in comparison to man they are not nearly as dangerous. Their attributes consists of a well-developed sensory network. Their senses include olfactory, tactile, auditory, vision, taste, and electroreception. Electroreception is a remarkable modality¹ because it enables the animal to detect electrical fields. The animals use this modality to locate their food and analyze their environment.

According to Theodore H. Bullock, a neuroscientist, "the prediction, discovery, and establishment of electroreceptors is of extreme interest not only for the intrinsic insight into the life of some elasmobranchs that see the world through a new sense but also for the lessons it teaches about identifying and classifying receptors by function." As a response to this statement, this article will address electroreception in elasmobranchs by examining the history of electroreception, the morphology² of electroreceptors, the physiological and behavioral evidence, and, lastly, the ways electroreception influences the behavior of these remarkable animals.

History of Electroreceptors

It is believed that the "electric" fish evolved from a pre-electric fish without electric organs but sensitive to electric fields. Furthermore, it is suggested that at that primitive stage, the electrosensitivity might have been used to detect the muscular potentials of prey, predators, and members of the same species (Kalmijn, 1971). The first evidence of electrosensitivity in elasmobranchs dates back to 1935 when Dijkgraaf, working on Scyliorhinus canicula, noticed the animal's sensitivity to a rusty steel wire (Dijkgraaf & Kalmijn, 1962). The experimenters approached the head of a blindfolded shark with such a wire. They observed that the animal escaped when the wire was closer than several centimeters from its head. They repeated the experiment with a glass rod, but the animal did not react to it. Dijkgraaf assumed that the shark was stimulated by the galvanic currents produced at the surface of the metal wire, but had no way of proving his assumption.

Dijkgraaf's hypothesis largely remained a speculation until Lissmann in 1958 formally suggested, based on behavioral evidence, that a group of receptors and central processes, called the ampullae of Lorenzini, aid in the detection and analysis of electric fields in the marine environment of fish. Later, experimenters verified the existence of the new class of specialized receptors through physiological experiments. They named them "electroreceptors" because their adequate stimuli³ were electric fields (Bullock et al. 1961, Kalmijn, 1966, 1971).

The Physical Stimulus for Electroreception

In oceans, electric fields are induced by both biological and geological causes. In the latter case electric fields are induced by water flowing or fish swimming through the earth's magnetic field by geomagnetic variations⁴ and by geophysical events⁵. The animals use these electric fields for navigation and identification of their environment.

Electric fields in the oceans can also be produced by marine animals. The internal and external electrochemical environments of marine animals differs. The difference creates a voltage gradient across the water skin boundary. The potential difference produces current loops which yield a bioelectric field in the surrounding waters. An animal's behavior can produce additional electric fields. For example, when a fish swims, muscles contract. Muscle contraction takes place when chemically-dependent channels, impermeable to sodium and potassium, open. The movement of such ions across the membrane produces an electric field that travels away from the animal in the conducting medium (salt water).

The number of muscle contractions affects the magnitude of the electric fields. If more muscles contract, the magnitude of the field is greater and vice versa. Furthermore, the intensity of the electric fields changes in the case of a wounded animal. For example, crustaceans can generate a voltage of 50.0 mV measured with a sensing electrode 1 mm away from the surface of the animal. The same crustacean, if wounded, generates a much higher voltage of 1250.0 mV (Kalmijn, 1974). H. S. Burr in 1947 established the presence of these bioelectric fields in the vicinity of marine animals (Kalmijn, 1974). These gradients can be easily detected by certain members of elasmobranchs.

Ampullae of Lorenzini

The ampullae of Lorenzini are complicated and extensive specialized skin sense organs characteristic of sharks and rays. The next four subsections of this article address the physical stimulus, the anatomy, and physiological characteristics of electroreceptors.

Anatomy

The ampullae of Lorenzini are electroreceptive units in sharks. They are jelly-filled canals found on the head of the animal which form a system of sense organs, each of which receives stimuli from the outside environment through the dermis and epidermis. Each canal ends in groups of small bulges lined by the sensory epithelium⁶. A small bundle of afferent nerve fibers innervates each ampullae⁷ ; there are no efferent fibers⁸ (Murray, 1974). The ampullae are mostly clustered into groups. The lengths of the canals vary from species to species. Even within any one fish, but the pattern of distribution is approximately species specific. An interesting anatomical observation is that the same number of nerve fibers are dedicated to electroreceptors as are dedicated to the eye, ear, and the lateral line (Murray, 1974). The number of nerves that innervate a sensory organ often determine the sensitivity and degree of acuity⁹ of that sensory organ. They also tell us about the relative importance of that sensory organ for an animal. Consequently, we can conclude that the ampullae of Lorenzini is at least as important to an animal as its eyes, ears, and the lateral line (Murray, 1974).

Physiological Characteristics

Murray's studies of electrophysiological characteristics in Raja and Scyliorhinus have demonstrated that the ampullae are sensitive to weak electric fields. In fact Scyliorhinus canicula can detect gradients as low as 1-µV/cm while the Raja can detect a 0.01-µV/cm. This means that Raja can detect a 1.5 V gradient (relative to ground) from about 1000 miles away (Kalmijn, 1974).

In one experiment Murray recorded the electrical activity from the ampullary nerves under water by stimulating them with electric fields produced by electrodes some distance away. He obtained the best results when the voltage gradient of the field was parallel to the ampullary canals. When the surface openings of the canals were made negative by a DC field, the response was an increase in the frequency of action potentials at the beginning and a decrease in the frequency at the termination of the stimulus. Murray also recorded from the lateral-line organs of the sharks and rays and found them not nearly as sensitive to electric fields as the ampullae of Lorenzini (Murray, 1974).

Role of Electroreception in Behavior

In 1971 Kalmijn looked at the feeding responses of the shark, Scyliorhinus canicula, and the ray, Raja clavata, toward the flatfish, Pleuronectes platessa. These experiments demonstrated that the animals make significant use of their sensitivity towards electric fields. A synopsis of these experiments follows.

First, the flatfish was introduced into a pool where the sharks and rays were maintained, and the flatfish was given enough time to bury itself in the sand. When the sharks and rays swam within 10-15 cm of the flatfish, the researchers observed that the animals attacked the spot where the fish was buried. Subsequently, the animals retrieved and consumed the fish.

Then, the fish was placed in an agar chamber to conceal it both mechanically and chemically without affecting the electric field of the animal. The agar chamber did not change the attack pattern of the sharks and rays. To prove that the 1 cm agar¹⁰ layer was thick enough to block the chemical scent of the animal, frozen pieces of fish were exchanged for live fish. Following this change, the animals did not attack the chamber. Next, the live flatfish was returned to the agar chamber and a thin electrically-insulating plastic film was placed above the chamber to block the electric field of the flatfish. Once again the sharks made no attempt to attack the flatfish. Finally, to provide direct evidence for the shark's and ray's ability to detect electric fields, two electrodes were buried under the sand, and a current was passed between them. The shark and ray exhibited the same attack pattern as when a live flatfish was buried under the sand.

These experiments suggest that detection of electric fields directly influences the feeding response of the animals. The behavioral evidence combined with the ability of the animals to detect electric fields in their natural environment leads to the conclusion that electroreception is a biologically significant modality to the animal.

Significance of Research

Electroreceptors enable the elasmobranchs to search and locate prey and navigate through the earth's ocean and seas. Electroreception allows these animals to sense the presence of their victims long before the victims have the chance to see their predators. This awesome advantage has made these animals into one of the most threatening predators on earth.

By understanding the sensory capabilities of the marine predators and stimuli emanated from their prey we can guard ourselves from hazards by building the proper repellents or shields¹¹. At the same time we protect the animals from the side which effects our technology by taking the necessary precautions. For example when ships or fishing nets are being built, engines could be shielded.

Unlike elasmobranchs, humans only possess five sensory modalities. Sometimes humans conclude incorrectly that marine animals use only the same five senses. The type of scientific research described in this article helps to clear up such misunderstandings, but also gives us a better understanding of the world in which we live.

References

Bullock, T. H. 1982. Electroreception. Annual Review of Neuroscience 5:121-70.

Bullock, T. H., Hagiwara, S., Kusano, K., Negishi, K. 1961. Evidence for a category of electroreceptors in the lateral line of gymnotid fishes. Science 134:1426-27.

Dijkgraaf, S., Kalmijn, A. J. 1962. Verhaltungsversuche zur Funktion der Lorenzinischen, Ampullen. Naturwissenschaften 49:400.

Kalmijn, A. J. 1966. Electro-perception in sharks and rays. Nature 212:1232-33.

Kalmijn, A. J. 1971. The Electric Sense of sharks and rays. Journal of Experimental Biology. 55:371-83.

Kalmijn, A. J. 1974. The Detection of Electric Fields from animate and Animate Sources Other Than Electric Organs. In: Handbook of Sensory Physiology., A. Fessard, (ed). Springer-Verlag, New York.

Murray, R. W. 1974. The Ampullae of Lorenzini. In: Handbook of Sensory Physiology., A. Fessard, (ed). Springer-Verlag, New York.

Stevens, W. K. The Odds of a Shark Attack. New York Times, December 8, 1992.

Footnotes

1 An avenue of sensation (Webster's Dictionary).

2 Morphology is the study of structure and form in plants and animals (Webster's Dictionary).

3 Adequate stimulus is the form of stimulus to which a sense organ is most sensitive.

4 Geomagnetic variation is the change in the fluctuating strength of earth's magnetic field.

5 An example of a geophysical event is the tectonic processes that cause strain variations in the earth's crust which lead to changes in the magnetization of rocks and local electric fields.

6 The sensory epithelium is a single layer of receptor and supporting cells.

7 Afferent nerve fibers carry information towards the central nervous system (Brain).

8 Efferent nerve fibers carry information towards the peripheral nervous system.

9 Acuity refers to the resolving power of the sensory organ.

10 Agar is a gelatinous colloidal extractive of a red alga (Webster's Dictionary).

11 The chance of being killed by a shark attack is less than the chance of being killed by a bee sting. There are 50 to 70 shark attacks every year worldwide. They result in five to ten deaths according to International Shark Attack file at the Florida Museum of Natural History (Stevens, 1993).